I'm sure Contador learned about Schleck's problem but not immediately as many here like to think. It's confusing on us, it's a bit more for the ds.
And it's ridiculous to say that it is only Contador's mistake and that Sanchez or Menchov just followed. I didn't see that, especially in the descent.
In any case, the half minute deficit that AC had was not an issue for Contador, but the 40'' that, for example, Menchov gained are very important for the Bordeaux TT.
I remember Pantani had the same problem, then he putted back the chain in place, he caught them all and he won.